Electrical snap-action switch



Nov. 19, 1963 H. BUNKE 3,111,565

ELECTRICAL SNAP-ACTION SWITCH Filed Aug. 21, 1961 IN VEN TOR.

BY M,WMVWW United States Patent 3,111,565 ELECTRICAL SNAP-ACTION SWITCHHorst Bunke, Oberkochen, Wurttemberg, Germany, as-

signor to Alfred Eckerfeld, Laugenberg, Rhineland,

Germany Filed Aug. 21, 1961, Ser. No. 135,098 Claims priority,application Germany Aug. 20, 1960 3 Claims. (Cl. 200-67) This inventionrelates to an electrical snap-action switch, in particular forelectrically heated apparatus such as continuous-flow heaters.Snap-action switches are well known in various modifications, wherein ashift lever can be moved through its dead center position and isconnected with a contact arm by means of a snap-action spring. In suchswitches, the snap-action spring changes its direction of operation andsuddenly moves the contact arm into its make or break direction, as soonas the shift lever passes through its dead center position. In manycases, in particular in power switches for electrically heatedapparatus, the shift lever must be actuated nonpositively by a movingmember such as the push rod of a diaphragm exposed to water pressure orby the expansion member'of a thermostat. If such a moving member makes aslow movement and this is the case as a rule, the shift lever isapproached to its dead center slowly. As a consequence, the contactpressure depending on the snap-action spring is decreased during theswitching-off operation and reaches the value of zero in the dead centerposition before the contact arm is lifted from the counter-contact bythe snap-action spring after the dead center position has been passedthrough. This means that with such a snap-action switch, an uncertaincontact tending to freezing together is obtained in the neighborhood ofthe dead center, if the shift lever is actuated non-positively by aslowly moved member.

The invention has for its object to maintain the full contact pressurein such a snap-action switch up to the moment of breaking, even withslow actuation of the shift lever.

According to the invention this is achieved in that the shift lever isblocked by a locking device in the make position of the contact arm, andthat the locking device can be released by the moving member liftingfrom the blocked contact arm, when this member moves past a positioncorresponding to the dead center of the shift lever. Thus the shiftlever is prevented by the locking device from following the slow movingmember during the switching-off movement, and is released only in thatmoment when the moving member has already moved backwards to such anextent that [a sudden breaking is effected. In principle, such anarrangement comprising a. locking device for maintaining the fullcontact pressure can be employed in all possible embodiments of suchdead center switches. The additional expenses required are extremelysmall. Advantageously the locking device comprises a spring loaded pawl,which can be released by a cam provided on the moving member.

An embodiment of the invention is shown more or less schematically, inthe accompanying drawing.

A shift lever 1 designed as a flexible blade and a contact arm 2 alsodesigned as a flexible blade of an inte gnal stamping is fixed at 3 tothe switch casing (not shown). A compression spring 4 is fixed betweenthe free end of the shift lever 1 and the contact arm 2. A push rod. 6acts on the shift lever -1 against the action of a return spring 5. Aspring loaded locking pawl 7 is pivotally mounted in the switch casing.Pawl 7 blocks the shift lever in the position shown. The locking pawlcan be released at a certain position of the push rod 6 by means of acam 8 provided on the push rod. Reference numeral 9 designates a stopfor the contact arm ice 2. The stationary counter contact 10 cooperateswith a contact 2' of the contact arm 2 to close the electric circuit.

In the embodiment shown the switch is actuated by the Water deficiencysafety device of an electrically heated continuous-flow heater. It will,of course, be understood that the invention is not limited to such orsimilar applications.

,The continuous-flow heater comprises a main body 11 provided with aU-shaped heating channel 12. A heating coil 13 is arranged in theheating channel 12. This coil is supplied with current from an A.C.current source 14 through the contacts 2', 10 of the switch described.Channels 15 and 16 are provided in series with theheating channel 12 atthe inlet and at the outlet side thereof. The heating coil is notinsulated and arranged in the water how, and the water columns in thechannels 15 and 16 constitute electric resistors which limit the leakagecurrents and make it possible to ground the inlet and the outlet of theapparatus. This principle of an electric continuous-flow heater is wellknown per se and forms no part of the present invention. A throttlescrew 17 is provided between channels 15 and 12.

A bell-shaped diaphragm casing 18 is placed on the main body 11. Themain body 11 is provided with a recess 19 on its top face. The recess isconnected with the channel 15 through a bore 20. A diaphragm 21 isclamped between the main body 11 and the diaphragm casing 18. The space22 above the diaphragm 21 is connected to the channel 16 through achannel 2.3 passing through the outer rim of the diaphragm 21.

The push rod 6 is passed through the diaphragm casing 16 by means of astuiiing box .24, and, at its lower end, carries a diaphragm plate whichcomes into contact with the diaphragm 21 under the influence of a spring26, if the diaphragm makes a stroke. The push rod 6 is provided with ashoulder stop 27 and is enclosed by the fork-shaped end of a leaf spring28 which rests on the shoulder 27 and is fixed at 29. A screw 30 presseson the spring 28. By means of screw 30 the spring 28 may be more or lesspre-tensioned.

The switch stop 9 is conducting part of the circuit and is connectedwith the contact 2 by a [flexible conductor 31.

The device described operates as follows:

If the tap valve (not shown) is opened, a dynamic pressure drop at thethrottle 17 is obtained in well known manner, which becomes effective onthe diaphragm in the spaces 19 and v22 through channels 20 and 23,respectively. The diaphragm makes a stroke and lifts the push rod :6against the action of the springs 26 and 28. By adjustment of the screw30' the pressure to which the deviceresponds can be varied in order topermit an accommodation to the local conditions. Upon closure of the tapvalve the pressure drop is decreased and the push rod 6 is moveddownwards under the influence of the springs 26 and 28.

In the make position shown of the contact arm, a sufficient contactpressure between the contacts 2, 10 is produced by the compressionspring 4. The push rod 6 non-positively abutting the shift lever 11 haslifted the lever 1 to such an extent that the locking pawl 7 has snappedin and blocks lever 1.

When the push-rod 6 has moved downwards the switch is to break. Withinitial movement, the push-rod 6 moves down away'from the blocked shiftlever 1. Only after a predetermined movement of the push rod '6, thelocking pawl 7 is released by means of cam '8. The shift lever 1 ismoved downwards under the influence of the return spring 5 and passesthrough its dead center in the plane of the contact spring 2. Duringthis operation, the compression spring changes its direction ofoperation and lifts the contact spring 2 from its counter contact 10 sothat it abuts the stop 9. It is essential that the release of the pawl 7is effected only when the push rod 6has passed through a positioncorresponding to the dead center position of the shift lever 1. By theblocking of the shift lever 1, the full contact pressure is maintainedup to the moment of breaking. The return spring can be omitted, if theshift lever 1 has suffi cient inherent elasticity.

Invention is claimed as follows:

1. In an electrical snap-action switch having a contact arm movablebetween switch-on and switch-off positions, a shift lever operativelyconnected to the contact arm and movable across a center position forover-the-center actuation of the contact arm, a moving member contactingthe shift lever for positive action to the switch-on position andmovable between switch-on and switch-off positions through a pointcorresponding to the center position of the shift lever, and meansurging the shift lever towards the switch-off position, the improvementcomprising: a releasable latch engaging the shift lever in the switch-onposition; and actuating means connected to the moving member to releasethe latch after the moving member has moved from the switch-on positionto beyond said point.

2. In a switch as set forth in claim wherein said latch comprises apivotally mounted pawl movable between a latched and an unlatohedposition and having a portion blocking the shift lever in the switch-onposition, and means connected to the pawl and urging the pawl to saidlatched position; and said actuating means comprises a cam connected tothe moving member and contacting said latch when in the latched positionto move the latch to the unlatched position.

3. An electrical snap-action switch including: a flexible contact armhaving a supported and an unsupported end; a flexible shift lever havinga supported and an unsupported end and having its supporttd end integralwith the supported end of the contact .arm; means fixedly mounting thesupported end of each of the arm and the lever with the unsupported endsextending in a common direction; resilient means interconnectingunsupported portions of the lever and arm, whereby as the lever is movedacross center from one side to the other side, the arm will move from aswitch-on to a switch-01f position and vice versa; a contact contactingthe arm when the arm is in the switch-on position; means operativelyconnected to the lever to urge the lever from said one side towards theother; an operating member positioned at the other side of the lever,said operating member being movable toward said one side to contact andmove the lever to said one side against said urging and to retractbeyond the center; a pivoted latch engaging the lever when the lever isat said one side; and a cam attached to the operating member to contactsaid latch and disengage it from the lever after said operating memberhas so moved beyond center from said one side.

References Cited in the file of this patent UNITED STATES PATENTS1,275,200 Barnum Aug. 13, 1918 1,284,930 Roberts Nov. 12, 1918'2,284,940 Baak June 2, 1942 2,376,634 Tellkamp May 22, 1945 2,720,564Soreng et a1. Oct. 1, 1955

1. IN AN ELECTRICAL SNAP-ACTION SWITCH HAVING A CONTACT ARM MOVABLEBETWEEN SWITCH-ON AND SWITCH-OFF POSITIONS, A SHIFT LEVER OPERATIVELYCONNECTED TO THE CONTACT ARM AND MOVABLE ACROSS A CENTER POSITION FOROVER-THE-CENTER ACTUATION OF THE CONTACT ARM, A MOVING MEMBER CONTACTINGTHE SHIFT LEVER FOR POSITIVE ACTION TO THE SWITCH-ON POSITION ANDMOVABLE BETWEEN SWITCH-ON AND SWITCH-OFF POSITIONS THROUGH A POINTCORRESPONDING TO THE CENTER POSITION OF THE SHIFT LEVER, AND MEANSURGING THE SHIFT LEVER TOWARDS THE SWITCH-OFF POSITION, THE IMPROVEMENTCOMPRISING: A RELEASABLE LATCH ENGAGING THE SHIFT LEVER IN THE SWITCH-ONPOSITION; AND ACTUATING MEANS CONNECTED TO THE MOVING MEMBER TO RELEASETHE LATCH AFTER THE MOVING MEMBER HAS MOVED FROM THE SWITCH-ON POSITIONTO BEYOND SAID POINT.